Apparatus for producing continuous steel strip or other section



April 14, 1970 K. CLAUS ETAL 3,505,706

APPARATUS FOR PRODUCING CONTINUOUS STEEL STRIP OR OTHER SECTION Filed Nov. 2, 1967 4 Sheets-Sheet l INVEN TOR. QARUS A 0A April 14, 1970 K. CLAUS ETAL 3,505,706

APPARATUS FOR PRODUCING CONTINUOUS STEEL STRIP OR OTHER SECTION Filed Nov. 2, 1967 4 Sheets-Sheet 2 JG aq- II I" April 14, 1970 K. CLAUS ETAL APPARATUS FOR PRODUCING CONTINUOUS STEEL STRIP OR OTHER SECTION 4 Sheets-Sheet 5 Filed NOV. 2, 1967 April 14, 1970' K. cLAus ETAL 3,505,706 APPARATUS FOR PRODUCING CONTINUOUS STEEL STRIP OR OTHER SECTION Filed Nov. 2, 1967 4 Sheets-Sheet L 6 Fig. 7

United States Patent US. Cl. 18-9 6 Claims ABSTRACT OF THE DISCLOSURE A rolling mill for rolling steel particles into dense strip, having a rotary furnace for heating the particles in a protective atmosphere and a device for metering the particles into the roll gap.

This application is a continuation-in-part of our pending application Ser. No. 494,839, filed Oct. 11, 1965, for Improvements in the Production of Welding Steel, now Patent No. 3,359,100.

This invention relates to a method for the production of continuous steel strip or other section. This was formerly produced from blooms made by the puddling process, or from ingot-steel or weld-steel scrap piled into fagots. It is characteristic of both methods that oxides of iron present were converted into liquid slags, and were squeezed out during deformation, such as forging, extrusion or rolling. For this, very high degrees of deformation were required. Nevertheless the slag inclusions could not always be removed to a suificient extent, so that a heterogeneous texture resulted, and the products no longer fulfilled present-day requirements. In addition, to this the method was associated with severe manuallabour, which, notwithstanding experimental research, could not be replaced by machines.

It is an object of the invention to provide apparatus for producing continuous steel section from steel particles using a rolling mill in such a manner that the particles can be metered sufficiently accurately to provide a uniform, dense product. It is another object of the invention to enable such steel strip to be produced continuously and reliably in a practically endless form, whether as fiat strip, or as profiled strip, in as simple and cheap 21 manner as possible.

This invention provides apparatus for producing continuous steel section from steel particles, comprising a stand for rolling the particles into a densified product, rotary tube heating means rotatable about an inclined axis, for heating the particles in a nonoxidising atmosphere, means for supplying the particles to the upper, inlet end of the rotary tube heating means, means for rotating the heating means, and a closed dosing means adjacent to and sealed to the lower, outlet end of the rotary tube heating means, for receiving the hot particles from the rotary tube heating means, metering their flow and guiding them to the roll stand gap.

The closed dosing means (which may comprise a hopper means or funnel above the roll stand rolling gap) can compensate for any irregularities in the discharge from the rotary tube heating means and prevent starvation of the mill. In practice, it is very difficult to achieve even, uniform discharge from a rotary tube furnace.

3,505,706 Patented Apr. 14, 1970 No dimension of the particles employed is normally to be greater than eight times the thickness of the strip to be produced. The preferred mesh size is at least 0.2 mm. The particles employed are to be preferably of similar size and of similar shape to one another, for instance substantially spherical or ellipsoidal or even needles. The particles may be cast (granules), deformed (shavings) or porous (iron sponge). When employing granules of spherical or like form, those are particularly preferable which have a diameter of not more than four times the thickness of the material of the strip to be produced.

The special production of such particles seems expensive as compared with the use, formerly customary, of scrap or blooms; but the advantages of using comparatively small particles are (compared to scrap or blooms) so considerable, particularly when they are of similar shape and of small size, that the production of such particles for carrying out the weld-steel method is economically profitable. Particles produced by granulating liquid steel by means of water under pressure have proved especially economical, and very suitable technically. Preferably a jet of cast steel is split up by means of a jet of water, this method is cheap, and the superficial oxidation thus arising is reversed during the subsequent deoxidation.

The advantage of employing such particles which are small compared to blooms resides in the fact that the work of deformation required for obtaining a satisfactory texture is not greater than is necessary. If the deformation is effected by rolling, the particles to be rolled, provided they are of the dimensions mentioned, lie reliably within the gripping angle of the rolls.

It is not absolutely essential to have a particularly high temperature when rolling the particles, since no slags need be present which must be fusible. To reduce the work of deformation, however, the particles, before being rolled, are if possible to be heated up to at least 600 C., but in any case not to a temperature above the melting point of the steel, say not to above 950 C. As soon as and for as long as the particles are heated up to at least 500 C., they are to be moved relatively to one another to prevent them sintering together. Such relative movements are obtained in the rotary tube heating means (a cylindrical kiln or oven), and a strong current of hot gas can be introduced into the path of the hot particles from the heating means to the roll stand.

Using a rolling mill, a completely continuous method of working can be obtained. In passing through the roll gap, the particles are not only compressed in an uninterrupted manner, but are also welded together. The gases present in the interstices between the particles escape, predominantly in a direction opposite to the direction of rolling.

When rolling metal powder, a high speed is not admissible, for at high peripheral speeds of the rolls such a strong current of gas or air arises that particles of the powder to be welded are carried away by it, thus leading to disturbances in the supply of material. Now it has been found that particles whose maximum dimension is at least 0.2. min, for instance granulate or iron sponge, can be successfully rolled at a peripheral roll speed of more than 0.2 metre per second and preferably more than 0.4 metre per second.

Iron granulate whose maximum particle dimension is preferably more than 0.5 mm., can be successfully rolled with a roll-periphery speed of from 1 to 1.5 metres per second, so that the production of strip or section becomes extremely economical. Steel granulate and iron sponge whose smallest particles have been sifted through a screen of 2 mm. width of mesh have been rolled at a peripheral speed of the rolls of from 1 to 1.5 metres per second. Observations made during the rolling showed that not the slightest disturbance occurred in the feeding of the material. It is therefore to be expected that the method will admit of being carried out even at substantially higher peripheral roll speeds.

The particles can be densified and welded in a single pair of rolls and in a single roll pass. By this means the dimensions and the cost of apparatus for the production of strips and sections are greatly reduced.

The strip or section produced according to this invention is not merely equal to that produced from ingot steel, but can also have special advantages in certain cases. On account of the irregular orientation of the particles used, this invention is particularly applicable to the production of transformer laminations and of metal sheets for deep drawing.

The carrying out of the method with the aid of a rolling mill will be described hereunder by way of example. The initial material may consist predominantly of ball-like granules of an average diameter of 2 mm.

The contaminations on the surfaces of such particles are primarily ferric oxide. These contaminations can be removed by any de-scaling method, for instance by projecting the particles at high speed against a plate. In the present connection bright annealing (i.e. heating in a de-oxidising atmosphere) has proved particularly advantageous, because it can be combined with the heating of the particles up to welding temperature and converts the oxides to iron, which is not lost. This method of deoxidation presents the special advantage that the heating can be effected in a reducing atmosphere, which precludes any oxidation. The bright annealing may be effected at above 600 C. when heating up tov a working temperature of from 900 to 1250 C., say 950 C. As a modification of this, the commencement of the heating may even be effected in an oxidising atmosphere, provided a suflicient deoxidation is then effected in a reducing atmosphere.

If the reducing gases contain hydrogen, it is possible to eliminate the oxides completely from the surfaces of the particles, since the water vapour that forms during the reduction can be drawn off without any trouble.

It is particularly advantageous to carry out the deoxidation and the heating in an inclined rotary cylindrical kiln, since owing to the incessant movements to which the particles are subjected in a cylindrical rotary kiln, any premature caking together is obviated. This operation may be carried out in a rotary cylindrical kiln, electrically heated, directly or indirectly, or indirectly heated by gas, with a reducing gas, for instance hydrogen, as the reducing agent. The heating could however, be more economically elfected in a directly gas-heated rotary cylindrical kiln, the deoxidation being obtained by suitable flame-regulation.

When the particle surfaces have been freed from oxides, it is necessary to supply the particles from the reducing kiln to the rolling mill in such a manner as to preclude reoxidation or contamination. For this purpose the kiln outlet is arranged over the roll gap of a vertical pass roll stand having its two roll axes in a substantially horizontal plane. The shortness of the time required for passing between the kiln outlet and the roll gap not only enables the oxidation to be kept small, but also guards against losses of heat. The path between the kiln outlet and the roll gap may furthermore be screened from the exterior by a protective casing, so that losses of heat and access of air are largely prevented. Protective gas can be supplied from the heating kiln within the pro tective casing to the roll gap at a pressure slightly above atmospheric.

As a particularly cheap reducing medium, partially burnt town gas or partially burnt natural gas has been found useful. This partially burnt town gas or natural gas may be used for reduction either immediately after the burning, or only after being dried. In the former case the heat of combustion may advantageously be utilised directly for heating up the parts to be welded. The partially burnt gas can be passed in countercurrent to the particles, and the kiln outlet can be located in the zone of maximum reducing action where there is an excess of high temperature deoxidising gases.

If a solid reducing agent is used, for instance coal dust or the carbon in the steel, inert gases, for instance nitrogen or argon, may be employed for protection against oxidation, and the heating may be effected indirectly, either electrically or by burning gas.

It has been found that it is not necessary to work under reducing conditions throughout the whole of the heating operation. It is sufficient that reducing conditions should prevail at least in the region of the kiln outlet, and that the particles should remain for a sufficient length of time in the reducing zone, or that the time of passage should be sufficiently long, to free the surfaces to an adequate extent from disturbing oxides.

The oxides are more deformable than the steel at the rolling temperature; thus if the oxide slag is present, it is squeezed out, often to form large areas separating the individual particles and preventing some of the particles welding together properly. For some products, the presence of the oxide is beneficial; in rolling, the oxide forms long stringers in the strip, improving the resistance of the strip to fatigue failure as do such stringers in wrought irons. In such circumstances, it is only necessary to prevent excessive oxide build-up.

However, for other products, the presence of the oxides requires great deformation in rolling in order to squeeze them out of the metal. If the oxides are removed, a comparatively small degree of deformation is sufiicient to produce steel strip of good quality. It has been found that a single roll pass is enough to attain complete densification, and hence a strip of satisfactory properties with no substantial inclusions of slag; with merchant bar or fagoted steel, a number of roll passes with intermediate re-heating were required in order to squeeze out all the slag.

The testing of steel strips that have been produced according to the invention has shown that the welds are by no means weak spots in a finished strip. For examp e, a strip about 2 mm. thick was tested. When tested to destruction it was found that the fracture did not extend along the original boundaries of the particles but transversely through the particles. The texture obtained by working in accordance with this invention is so uniform that its micrograph could hardly be distinguished from that of conventional ingot steel even by a technologist. Whilst the properties of the old rolled, welded steel were for the most part dependent upon direction, because the longitudinal material to be Welded was laid in the direc tion of rolling, this is not applicable according to the present invention. When the particles have a diameter of less than 2 mm., the steel produced does not show, even subsequently, any pronounced texture, presumably because the particles have undergone only a relatively trifling deformation. The steel produced according to this invention has therefore proved satisfactory in the cupping test. In particular, hardly and formation of lobes or peaks oc curs. The method is therefore articularly suitable for the production of transformer laminations.

In the usual production of welded steel, by rolling, only great thickness of material have been obtained in the first pass. With the use of small particles according to the present invention, small thicknesses can be obtained even in the first pass. Consequently, it is possible, according to the invention, to produce finished products with a single roll pass. It is therefore possible, with a single roll stand, to produce finished products successfully from the initial material without keeping the total deformation less than is necessary for obtaining a good quality. In a single pass, from granules of a diameter of less than about 2 mm., strips of a thickness of 1.3 mm. have been successfully produced, and this in such a way that no additional deformation was necessary. By employing relatively thin rolls, and smaller particles, still smaller thickneses of steel strip are obtainable in one pass.

If the particles are kept small, in the sense indicated above, the fagoting or piling of the initial material that is otherwise necessary in welding is omitted. If however, larger particles are employed according to the invention, it may happen that not enough particles are simultaneously engaged by the rolls. In order to remedy this defect, either the particles are bunched, and, it may be, impelled into the roll gap under pressure, or else rolls are used which are of such large diameters that suflicient particles are engaged at the same time. Using the invention, a continuous method of working can be obtained right from the heating kiln to the reel or the cooling bed. The production of ball-like particles can also be included in the process, so that a continuous production line is possible from the smelting furnace, through the apparatus for the production of the particles, right to the reel or the cooling bed.

Two constructional examples of the invention are illustrated in the accompanying drawings, in which:

FIGURE 1 shows apparatus with a kiln or oven which is indirectly heated electrically and in which the protective gas may be assumed to consist for instance of hydrogen gas;

FIGURE 2 shows apparatus in which the protective gas consisting for instance of partially burnt town gas, also serves for heating the granulate;

FIGURE 3 shows the kiln outlet, and the rolling mill arranged thereunder;

FIGURE 4 shows a partial section of FIGURE 3;

FIGURE 5 shows a view looking in the direction of the roll axes of the apparatus for supplying the parts to be welded into the roll gap of a rolling mill;

FIGURE 6 shows a -view partly in section on the line VI-VI looking in the direction of the arrow A in FIG- URE 5; and

FIGURE 7 shows a plan of the rolling mill of FIG- URES 5 and 6.

According to FIGURE 1, the granulate, through a tube 1, is filled into a hopper 2, which opens into a rotatable tube 3, which is journalled and sealed at rotary passageways 4 and 5. The other end of the tube 3 opens by way of the rotary passageway 5 into an intermediate container 6, with an associated hopper or funnel 6a. In practice, it is generally impossible to operate the rotary tube 3 so that it gives a uniform rate of discharge; the hopper or funnel 6a acts as a metering device to prevent starvation of the rolls of the rolling mill. The rotatable tube 3 is surrounded by an electrical heating appliance 7. The lower end of the hopper 2 is so dimensioned that a substantially uniform flow, limited as regards quantity, of granulate 8, passes through the tube 3. Usual dosing appliances, vibratory conveyors or strip-weighing means may also be provided, in order to obtain a uniform flow of the granulate. The granulate, heated and reduced in the tube 3, flows into the container 6, the connection of which with the tube 3 is sealed against external air. The container 6, by its hopper 60, opens immediately above the roll gap, which is formed by two rolls 9 and 9a. The hopper is so shaped that as little gas as possible, which is admitted at a raised pressure into the hopper 6a, can escape from the interstices between the hopper 6a and the rolls 9 and 9a. The rolls 9 and 9a may be driven in the usual manner. A rolled strip 10 produced by them is bent round and guided on to a roller bed 11, upon which it can run either straight on as a strip 11a, or from which it is transferred to a winding means 12. The latter is to be preferred when it is a question of a flat strip; but the arrangement of the strip 11a is preferable when it is a question of profile strips.

At 13, protective gas is introduced into the hopper 6a, this being a gas which has a deoxidising action, and which consequently withdraws oxygen from the heated granulate. It is preferable to employ hydrogen gas. Inside the space enclosed by the members 3 and 6 a raised pressure is formed, so that air cannot enter the spaces 3 and 6 from any point. Where no complete sealing can be effected, for instance in the region of the roll gap or at the mouth of the hopper 8 where it discharges into the tube 3, some hydrogen still escapes, owing to the raised pressure, but this can burn harmlessly in the atmosphere.

The hopper 8 is always kept so full as to form a pressure brake, which secures the desired raised pressure in the tube 3. From the aperture 1, excess protective gas escapes, and can be burnt from there or from a special burner, or supplied for some other utilisation.

In order that in the roll gap any reoxidation of the granulate may be substantially prevented, the hopper for supplying the granulate to the roll gap may advantageously be of the construction shown in FIGURES 5, 6 and 7.

In these figures, denotes the rolls, in the roll gap 91 of which metal particles or granules 92 are welded into a section 93, in the present case a strip. The granules 92 are supplied to the roll gap 91 by a feeding device 60, constructed as a hopper, which consists of two lateral boundary walls 61 and 62, and two boundary walls 63 and 64 extending parallel to the roll axes 94. The lateral boundary walls 61 and 62 are shaped to fit the peripheries of the rolls 90. The boundary walls 63 and 64 extend right to the roll surfaces 95. The feeding device 60 is enclosed in or surrounded by a chamber 65 filled with a protective gas. The protective gas flows through pipes 66 and 67 to the chamber 65, which consists, like the feeding devices 60, of two lateral boundary walls 68 and 69, and two boundary walls 70 and 71 extending parallel to the roll axes 94. The lateral boundary walls 68 and 69 are likewise adapted to the peripheries of the rolls 90, and extend approximately to the roll gap 91. The chamber is closed above by a top wall or cover 72, whereas in the region of the rolls it is open for the escape of the protective gas. On the under side of the rolls a further chamber 73 is provided, which is likewise filled with protective gas through supply pipes 74, so that the finished rolled product that issues, in the present case the strip 93, is guided through this atmosphere of protective gas. This reliably prevents atmospheric oxygen passing from this side of the rolls through the roll gap to the granulates 92 that have not yet been treated.

In the constructional example of FIGURE 2, the granulate is thrown into a hopper 20, from which it flows to a dosing appliance 21, out of which it passes into a tubular nozzle 22 of a rotary cylindrical kiln or oven 23, 24 and 25. The parts 24 and 25 of the rotary cylindrical kiln are non-rotatable, and are sealed in relation to the rotatable part 23. The part 23 is supported upon rollers 26 and 27, and carries a toothed rim 28, which, by way of a pinion 29, is driven by an electric motor 30.

On the nonrotatable part 25 of the rotary cylindrical kiln is mounted an outlet hopper or funnel 36, which supplies the heated granulate to the working rolls 37a, 37b of a rolling mill. The hopper or funnel 36 meters the flow of granulate to the rolls. The working rolls of the mill are supported by backing rolls 38a and 38b. The strip 39 formed in the gap between the rolls 37a and 37b is cooled by sprinklers 40 and 41, and is at the same time bent round. For this purpose the rollers of a roller bed are arranged between the sprinklers 40. The strip then runs to a driving appliance 42, beyond which a further cooling means may be arranged. There may then follow the usual devices, such as shears, winding machines and the like.

Into the part 25 of the kiln there opens at 43 an air pipe and a gas pipe, which force coal gas and air at an appropriately raised pressure into burners arranged in the part 25. This partly burnt town gas passes to the left from the part 25 on to steel granulate which is already preheated, beats it further, and thoroughly deoxidises it. The products of combustion pass out at 22, and may be conveyed from there to a chimney, a heat-exchanger or the like. The granulate travelling in from the left is therefore preheated.

For example, the granulate may have an average particle diameter of about 1 to 2 mm. Such granulate can be rolled substantially more quickly than powder, so that the rolls 37a and 37b and the rolls 9 and 9a revolve at a peripheral speed of more than 1 metre per second, preferably from 1 to 1.5 metres per second. At such speeds, powder would come whirling out of the rolling mill. The rolling speed may be kept much higher than in installations which cold-roll so-called green strip and then supply it to an annealing furnace (sintering furnace), since such sintering furnaces, at a rolling speed according to this invention, would have to be of practically intolerable length.

Since a raised pressure prevails in the rotary cylindrical kiln, protective gas also passes into the hopper 36, and protects the granulate against oxidation until it enters the roll gap.

Obviously it is also possible to employ roll stands the roll axes of which do not lie in a horizontal plane, but in a vertical plane for example.

In order to obviate an adjusting of the rolls under pressure, and to enable the kiln to be operated undisturbed during a brief interruption in the operation of the rolling mill, for the maintenance of constant temperature and passage conditions of the granulate, thus keeping it always ready for operation, in a further development of the invention, in the intermediate container 44 of FIGURE 3, which is arranged between the rotatable tube 45 and the pair of rolls 46, a lateral aperture 47 is provided, which co-operates with a flap valve 48 or a wedge 48' (FIGURE 4) in such a way that during the rocking of the flap valve 48 or the pushing of the wedge 48 into the fiow of particles 49, these particles emerge wholly or partly from the lateral by-pass aperture 47 (FIGURE 3) or 47' (FIGURE 4) of the intermediate container 44. The outfiowing current of particles 49' is then discharged, out of reach of the rolling mill, by way of the by-pass 50.

A further advantage of the by-pass resides in the fact that in the event of a relatively long disturbance of the rolling mill the kiln can be emptied Without the stock having to be passed through the rolls. Repairs can then be carried out immediately on the rolling mill without hindrance.

EXAMPLE An iron granulate was prepared having an average grain size of 3 mm. and the following chemical composition:

Percent Si Trace Cu 0.04 Al, dissolved 0.002

The thickness of the rolled strip was 1.8 mm., and it had a tensile strength of 37 kg./mm. and an extension (at break) of 34%. These tensile properties correspond fully to those of a strip of the same chemical composition which has been formed in the normal manner by rolling down a large billet in a number of roll passes. The strip was fully densified, with the exception of the voids that are always present in all such strip.

We claim:

1. Apparatus for producing continuous steel section from steel particles, comprising a roll stand for rolling the particles into a densified product,

rotary tube heating means higher than the roll stand and rotatable about an inclined axis, for heating the particles in a non-oxidising atmosphere,

means for supplying the particles to the upper, inlet end of the rotary tube heating means,

means for rotating the heating means,

a closed dosing means adjacent to and sealed to the lower, outlet end of the rotary tube heating means, for receiving the hot particles from the rotary tube heating means, metering their flow, and guiding them to the roll stand gap, the dosing means comprising a hopper means above the roll stand gap,

and means for pressurizing the rotary tube heating means and the dosing means.

2. Apparatus according to claim 1, and including means for passing hot, non-oxidising gas up the rotary tube heat ing means in countercurrent to the steel particles passing down the rotary tube heating means.

3. Apparatus according to claim 1, and including a burner adjacent the lower end of the rotary tube heating means and means for passing combustible gas and air into the burner.

4. Apparatus according to claim 1, and including means for passing a non-oxidising gas into the rotary tube heating means, and wherein the rotary tube heating means has an inlet opening for the steel particles, the inlet opening being in sealing connection with a closed container in turn connected to a hopper for the supply of steel particles to the rotary tube heating means, the closed container having an opening for discharging the non-oxdising gas. 7 5. Apparatus according to claim 1, wherein the dosing means comprises a by-pass device provided between the lower,- outlet end of the rotary tube heating means and the roll-gap of the roll stand, to enable at least a proportion of the particle flow to be diverted away from the roll-gap, the by-pass device comprising a generally vertical main passage for falling steel particles, a downwardly inclined by-pass passage forking off the main passage, and a movable deflector member for deflecting some or all of the particle flow into the by-pass passage.

6. Apparatus according to claim 1, comprising means controlling said dosing means and the roll gap of said roll stand to form a fully densified product from steel particles having a mesh size of at least 0.2 mm. means controlling said rotary tube heating means to heat said steel particles to a temerature of 600 C. to 950 C., and means controlling the speed of rotation of the rolls of said roll stand to give a peripheral roll speed greater than 0.2 metre per second.

References Cited UNITED STATES PATENTS 1,542,119 6/1925 Wheatley 18-9 XR 2,158,461 5/1939 Koehring et a1. 2,350,179 5/ 1944 Marvin. 2,601,712 7/1952 Keys 189 XR 2,675,304 4/ 1954 Komarels 18-9 XR 2,771,637 11/1956 Silvasy et a1 18-9 XR 2,882,554 4/1959 Heck 18-9 3,114,930 12/1963 Oldham et a1 18-9 XR 3,366,717 1/1968 Rohaus 189 XR WILLIAM J. STEPHENSON, Primary Examiner US. Cl. X.R. '18--4 

